The invention relates generally to a method of soldering, and more particularly to a method of soldering together metallic terminals, such as those found in a fuel injector.
Soldering has long been used for joining together metallic components. In its basic practice, at least two metallic components to be joined are heated to an elevated temperature. The components must be heated to the required temperature such that the solder wire melts upon contact with the heated components. As the solder wire melts, it begins to flow and exhibits a xe2x80x9cwettingxe2x80x9d behavior as the flow moves along the surfaces of the joined components. Often, the quality of the soldered joint is dependent upon the wetting behavior of the solder flow. More specifically, the mechanical and electrical properties of the soldered joint are dependent upon achieving the proper wetting behavior of the solder flow.
For optimum solder flow, the components to be joined should be simultaneously and as evenly heated as possible. As a result, temperature gradients within and between the components are decreased and the temperature distribution within and between the components is substantially homogeneous.
Contact-type soldering techniques often do not yield a substantially homogeneous temperature distribution within and between the components to be joined. Such contact-type soldering techniques can include using a soldering iron or a similar tool to apply heat via a direct point contact to the components to be joined. Typically, the portion of the component in direct contact with the tip of the soldering iron has the highest temperature, while the portion of the component farthest from the point of contact with the soldering iron has the lowest temperature. The difference in temperature within and between the components to be joined yields a temperature gradient that can have a negative effect on the solder flow and the quality of the soldered joint.
Another soldering technique, non-contact laser soldering, provides some advantages over contact soldering techniques. With non-contact laser soldering, the laser beam can strike a larger area of the components to be joined, therefore decreasing the temperature gradient within and between those components. However, in applications where the laser beam is prevented from directly striking one of the components, a temperature gradient still results between the components.
Additional problems in the general practice of soldering can include positioning and guiding the solder wire to the desired location relative to the components to be joined. This is especially a problem in applications requiring automation, rather than manpower. While humans can manually adjust the location of the solder wire to attain the desired solder flow, achieving this control within an automated system is complicated and very expensive.
The invention provides for significant improvement to a method of soldering metallic terminals. The invention provides a method of soldering using a non-contacting heat source, such as a laser, to heat the components to be joined. The components are configured to aid in their heating and to guide the solder wire to an optimum location with respect to the components.
More specifically, the invention provides a method of joining together first and second electrical terminals. The method includes providing the second terminal with an aperture extending therethrough, positioning the first and second terminals in overlapping relationship with one another to provide access to the first terminal through the aperture in the second terminal, applying heat to the first terminal through the aperture in the second terminal to heat the first and second terminals, and positioning a solder wire in engagement with at least one of the heated first and second terminals to melt the solder wire and to form a solder pool that contacts the first and second terminals. This method substantially improves the heat transfer through the terminals and decreases the temperature gradient throughout and between the terminals, thereby improving the quality of the soldered joint.
In one aspect of the invention, applying heat includes directing a beam through the aperture to strike the first terminal and having at least a portion of the beam reflect off the first terminal to strike the second terminal adjacent the aperture to heat the second terminal. The beam can be generated by suitable lasers, including a solid-state laser, a gas laser, an excimer laser, a dye laser, or a semiconductor laser.
In another aspect of the invention, the first terminal is coupled to a fuel injector and the method further includes placing the fuel injector in a fixture to secure the fuel injector before applying heat to the first and second terminals. The second terminal is coupled to a retainer clip and the method further includes placing the retainer clip on the fuel injector to position the second terminal in overlapping relationship with the first terminal.
The invention also provides another method of joining together first and second electrical terminals. The method includes providing the second terminal with a notch therein, positioning the first and second terminals in overlapping relationship with one another so the notch overlaps the first terminal, providing a solder wire having an end, positioning the end of the solder wire in engagement with the notch of the second terminal to locate the solder wire with respect to the terminals, and melting the solder wire to form a solder pool that contacts the first and second terminals. This method provides a guide for the solder wire so that the solder flow is consistently developed in the desired location.
In one aspect of the invention, positioning the end of the solder wire in the notch includes feeding the solder wire from a solder feeding machine. The notch is sized to receive the end of the solder wire.
The invention further provides a method of joining together first and second electrical terminals using a combination of the methods described above. The method includes providing the second terminal with an aperture extending therethrough and a notch therein, positioning the first and second terminals in overlapping relationship with one another so the aperture overlaps the first terminal to provide access to the first terminal through the second terminal and so the notch overlaps the first terminal, applying heat to the first terminal through the aperture in the second terminal to heat the first and second terminals, providing a solder wire having an end, positioning the end of the solder wire in engagement with the notch of the heated second terminal to locate the solder wire with respect to the terminals, and to melt the solder wire to form a solder pool that contacts the first and second terminals.
Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims, and drawings.